Aperiodicity in the near field of full-scale rotor blade tip vortices

Kindler, Kolja; Mülleners, Karen; Richard, Hugues; Wall, Berend G. van der; Raffel, Markus

doi:10.1007/s00348-010-1016-8

Cited by 35 publications

(14 citation statements)

References 28 publications

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“…Corrections for this were implemented here using an integral-based approach (the Γ 1 method) that allowed for the vortex centres to be identified; the details of this are described elsewhere (Graftieaux, Michard & Grosjean 2001;Mula et al 2013). Previous studies using multi-bladed rotors have shown the vortex wandering motion to be anisotropic (Kindler, Mulleners & Richard 2010;Mula et al 2013). Similar results are observed here, where figure 2(c) shows the standard deviation of wander along the principal major and minor axes across all vortex ages.…”

Section: Vortex Characteristicssupporting

confidence: 79%

A study of the turbulence within a spiralling vortex filament using proper orthogonal decomposition

Mula

Tinney

2015

J. Fluid Mech.

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The stability and turbulence characteristics of a vortex filament emanating from a single-bladed rotor in hover are investigated using proper orthogonal decomposition (POD). The rotor is operated at a tip chord Reynolds number and tip Mach number of 218 000 and 0.23, respectively, and with a blade loading of C T /σ = 0.066. Inplane components of the velocity field (normal to the axis of the vortex filament) are captured by way of two-dimensional particle image velocimetry with corrections for vortex wander being performed using the Γ 1 method. The first POD mode alone is found to encompass nearly 75 % of the energy for all vortex ages studied and is determined using a grid of sufficient resolution to avoid numerical integration errors in the decomposition. The findings reveal an equal balance between the axisymmetric and helical modes during vortex roll-up, which immediately transitions to helical mode dominance at all other vortex ages. This helical mode is one of the modes of the elliptic instability. The spatial eigenfunctions of the first few Fourier-azimuthal modes associated with the most energetic POD mode is shown to be sensitive to the choice of the wander correction technique used. Higher Fourier-azimuthal modes are observed in the outer portions of the vortex and appeared not to be affected by the choice of the wander correction technique used.

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Section: Vortex Characteristicssupporting

confidence: 79%

A study of the turbulence within a spiralling vortex filament using proper orthogonal decomposition

Mula

Tinney

2015

J. Fluid Mech.

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“…These findings were consistent with the earlier analytical studies developed on a single helical filament by Widnall (1972). 32 PIV investigations by Kindler et al (2010) 13 and Mula et al (2013) 22 revealed an anisotropic nature of long-wave perturbations (vortex wander) on a plane perpendicular to the vortex filament axis. Further, such an anisotropic nature was found to be insensitive to the choice of the vortex center identification technique.…”

Section: Introductionsupporting

confidence: 91%

“…Mathematical details of the technique are well described by Graftieaux et al (2001) 9 and Kindler et al (2010). 13 Being an integral based approach, the results are not corrupted by noise introduced by gradients of the velocity field. However, the vortex center still relies on an accurate assessment of the velocity inside the vortex core where seeding is poor.…”

Section: A Facility and Instrumentationmentioning

confidence: 99%

Classical and snapshot forms of the POD technique applied to a helical vortex filament

Mula

Tinney²

2014

32nd AIAA Applied Aerodynamics Conference

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Low-dimensional characteristics of a helical vortex filament from a reduced-scale rotor are investigated using proper orthogonal decomposition (POD). Measurements are captured by way of particle image velocimetry. Experiments are performed on a 1.0 m diameter, single-bladed rotor in hover. The rotor is operated at 1500 RPM, which corresponds to a blade tip chord Reynolds number of 218,000 and a tip Mach number of 0.23. The blade is set to a collective pitch angle of 7.3 • , which resulted in a blade loading (C T /σ) of 0.066. Classical and snapshot techniques of POD are applied to a helical vortex filament, both of which revealed similar characteristics of the dominant modes. Two different techniques (Γ 1 and geometric center methods) of wander correction are applied to test the sensitivity of the low-dimensional characteristics using POD. Using the Γ 1 method, POD revealed that an elliptic instability dominated the energy spectrum of the velocity fluctuations within the tip vortex. However, at early vortex ages an axisymmetric mode, which is found to perform vortex roll-up, is found to be equally dominant. Further, the spatial structures of the most energetic modes derived from POD are found to be sensitive to the choice of the centering technique used.

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“…Substituting T ij ¼ u i u j þ ij ½ð p À p 0 Þ À c 2 ð À 0 Þ À ij into equation (8), we get the following equation:…”

Section: Fem Simulation Of Aerodynamic Noisementioning

confidence: 99%

Study on the aerodynamic noise of internal flow of regenerative flow compressors for a fuel-cell car

Kang

Zuo

Wei

2013

Proceedings of the Institution of Mechanical Engineers, Part C:

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The regenerative flow compressor used in fuel-cell cars generates high aerodynamic noise, which is the main source of noise. Compared with the research on centrifugal or axial turbomachinery, research on the noise of regenerative flow compressors is far from adequate. This paper presents the on-going work on it at Tongji University based on both experimental and computational works. In this study, a three-dimensional unsteady computational fluid dynamic model of the compressor was constructed with the large eddy approach. The pressure fluctuation, vortex noise source and Ffowcs William-Hawkings (FW-H) method were used to analyze the characteristics of the aerodynamic noise sources. Additionally, the far-field aerodynamic noise generated by the internal flow of the compressor was predicted using the aeroacoustic finite element method. The simulation results were validated with the experimental data. It was found that combining the fluid dynamic model and aeroacoustic finite element analysis promising results for aerodynamic noise prediction of compressors could be produced. The effects of the impeller parameters on the aerodynamic noise of the compressor were also studied.

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Aperiodicity in the near field of full-scale rotor blade tip vortices

Cited by 35 publications

References 28 publications

A study of the turbulence within a spiralling vortex filament using proper orthogonal decomposition

A study of the turbulence within a spiralling vortex filament using proper orthogonal decomposition

Classical and snapshot forms of the POD technique applied to a helical vortex filament

Study on the aerodynamic noise of internal flow of regenerative flow compressors for a fuel-cell car

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